The present invention is related to a novel surfactant for use in enhanced oil recovery. In particular, the present invention is directed to alky/aryl alcohols having been sulfonated on the aromatic ring with the alcohol having an alkyl branched side chain.
The present surfactants are also useful in many industrial applications, such as acid and alkaline cleaners and degreasers, acid pickling baths, textile scouring agents, fiber processing aids, scale inhibition, and metal plating.
In the recovery of oil from oil bearing reservoirs, it is usually possible to recover only minor portions of the original oil by so called primary recovery methods which utilize only the natural forces present in the reservoir. A variety of supplementary recovery techniques have been employed in order to increase the recovery of oil from subterranean reservoirs. The most widely used supplemental recovery technique is water flooding which involves injection of water into the reservoir. As the water passes through the reservoir, it acts to displace the oil trapped in the reservoir system leading to an enhanced recovery of oil.
It has long been recognized that factors such as interfacial tension between the injected water and the reservoir oil, the relative mobilities of the reservoir oil and injected water, and the wettability characteristics of the rock surfaces within the reservoir are factors which influence the amount of oil recovered by water flooding. It has been proposed to add surfactants to the flood water in order to lower the oil-water interfacial tension and/or to alter the wettability characteristics of the reservoir rock. Processes which involve the injection of aqueous surfactant solutions are commonly referred to as surfactant water-flooding or as low tension water-flooding. Also, it has been proposed to add viscosifiers such as polymeric thickening agents to all or part of the injected water in order to increase the viscosity thereof, thus decreasing the mobility ratio between the injected water and oil and improving the sweep efficiency of the water-flood.
A problem with stability and effectiveness arises with these products when they are used in environments characterized by temperatures in the range of 70.degree. C. to 120 C. and above, high pressures (e.g. 4,000 psi), and high concentrations of divalent metals such as calcium, magnesium, etc. (e.g. up to 3,000 ppm or more) and high salt content.
Many water-flooding applications have employed anionic surfactants. For example, a paper by W. R. Foster entitled "A Low-Tension water-flooding Process," Journal of Petroleum Technology, Vol. 25, February 1973, pages 205-210, describe the technique involved in the injection of an aqueous solution of petroleum sulfonates within designated equivalent weight ranges and under controlled conditions. The petroleum sulfonate plug is followed by a thickened water plug which contains a viscosifier such as a water soluble biopolymer. This thickened plug is then following by a driving fluid such as a field brine which is injected as necessary to carry the process to conclusion.
One problem encountered in water-flooding with certain anionic surfactants such as the petroleum sulfonate is the lack of stability of the surfactants in so-called "hard water" environments. These surfactants tend to precipitate from solution in the presence of relatively low concentrations of divalent metal ions such as calcium and magnesium. For example, divalent metal ion concentrations of about 50-100 ppm and above usually tend to cause precipitation of petroleum sulfonates.
Nonionic surfactants such as polyethoxylated alkyl phenols, polyethoxylated aliphatic alcohols, carboxylic esters, carboxylic amides, and polyoxylethylene fatty acid amides, have a somewhat higher tolerance to polyvalent ions such as calcium or magnesium than do the more commonly utilized anionic surfactants. While it is technically feasible to employ the nonionic surfactant solution to decrease the interfacial tension between the border displacement medium and petroleum contained in the reservoir such use is generally not economically feasible for several reasons. First, nonionic surfactants are not as effective on a per mole basis as are the more commonly anionic surfactants and, additionally, the nonionic surfactants generally have a higher cost per unit weight than do the anionic surfactants.
The use of certain combination of anionic and nonionic surfactants to combat hard water formations has also been suggested. For example, U.S. Pat. No. 3,811,505 discloses the use of alkyl or alkylaryl sulfonates or phosphates and polyethoxylated alkyl phenols. U.S. Pat. No. 3,811,504 and 3,811,507 disclose other surfactants used for this type of oil recovery.
The use of certain amphoteric surfactants which function as cationics in acid medium and become anionic when incorporated in alkaline systems has also been suggested. For example, U.S. Pat. No. 3,939,911 discloses a surfactant water-flooding system employing a three component surfactant system. This surfactant system includes an alkyl or alkylaryl sulfonate such as an ammonium dodecyl benzene sulfonate, a phosphate ester sulfonate and a sulfonated betaine. Finally, the use of hydrocarbyl-substituted polyoxyalkylene sulfonates has been disclosed in U.S. Pat. Nos. 3,916,994; 4,181,178; 4,231,427; 4,269,271; 4,270,607; 4,296,812; 4,307,782; 4,316,809; 4,485,873; and 4,478,281.
Recently, U.S. Pat. Nos. 4,468,335 and 4,468,342 have issued which disclose the use of branched alkyl-substituted polyethoxy propane sulfonates used for enhanced oil recovery. In addition, U.S. Pat. No. 4,469,605 to Stapp et. al has disclosed the use of sulfonated phenolic compounds as well as sulfomethylated compounds as surfactant systems in post oil recovery procedures.
While many surfactant water-flooding methods have been disclosed there is a substantial unfilled need for surfactants and water-flooding methods employing such surfactants that are useful in recovering oil from subterranean formations wherein the surfactant employed are suitable in harsh environments, in particular, environments where there is a high concentration of divalent ions such as magnesium and calcium. The present invention offers surfactants suitable in this type of environment.